I have been a GNU/Linux user for about 15 years. During that time, I have alternated between Arch and Gentoo.

Gentoo is very time consuming and complex, and Arch is a pain to keep clean. However, the ability to customize the system to your preferred configuration is a big draw for both.

For a light user like me, patching and customizing to PKGBUILD is just fine. Personally, I sometimes wish for something like the USE flag in Portage.

For a university assignment, I built a compiler for x86; I cheated a bit by relying on LLVM, but it gave me a better understanding of the architecture. I also developed emulators for the NES (Ricoh 2A03) and RISC-V (RV32I) as a hobby. For the latter, I implemented it in FPGA.